U.S. patent application number 15/676646 was filed with the patent office on 2018-01-11 for subcooling system with thermal storage.
The applicant listed for this patent is Johnson Controls Technology Company. Invention is credited to William L. Kopko, Satheesh Kulankara, Andrew M. Welch.
Application Number | 20180010838 15/676646 |
Document ID | / |
Family ID | 51521114 |
Filed Date | 2018-01-11 |
United States Patent
Application |
20180010838 |
Kind Code |
A1 |
Kopko; William L. ; et
al. |
January 11, 2018 |
SUBCOOLING SYSTEM WITH THERMAL STORAGE
Abstract
Embodiments of the present disclosure are directed toward
systems and method for cooling a refrigerant flow of a refrigerant
circuit with a cool water flow from a cool water storage to
generate a warm water flow and to cool the refrigerant flow by a
subcooling temperature difference, flowing the warm water flow to
the cool water storage, and thermally isolating the warm water flow
from the cool water flow in the cool water storage.
Inventors: |
Kopko; William L.; (Jacobus,
PA) ; Welch; Andrew M.; (Mount Wolf, PA) ;
Kulankara; Satheesh; (York, PA) |
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Applicant: |
Name |
City |
State |
Country |
Type |
Johnson Controls Technology Company |
Holland |
MI |
US |
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|
Family ID: |
51521114 |
Appl. No.: |
15/676646 |
Filed: |
August 14, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14203251 |
Mar 10, 2014 |
9733005 |
|
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15676646 |
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61793632 |
Mar 15, 2013 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F25B 40/02 20130101;
F25B 2700/21163 20130101; F28D 20/0039 20130101; Y02E 60/142
20130101; F25B 2700/21161 20130101; F25D 3/005 20130101; F28D
2021/0068 20130101; Y02B 30/745 20130101; F25B 41/00 20130101; F25B
2700/21162 20130101; F25B 2600/13 20130101; F25B 25/005 20130101;
Y02E 60/14 20130101; F28D 2020/0095 20130101; Y02B 30/70
20130101 |
International
Class: |
F25D 3/00 20060101
F25D003/00; F28D 20/00 20060101 F28D020/00; F25B 40/02 20060101
F25B040/02; F25B 41/00 20060101 F25B041/00 |
Claims
1. A subcooling circuit, comprising: a thermal storage unit
configured to store a cool fluid; a heat exchanger configured to
transfer heat between a cool fluid flow of the thermal storage unit
and a refrigerant of a cooling system; and a pump configured to
pump the cool fluid flow through the subcooling circuit, wherein
the thermal storage unit is configured to receive the cool fluid
flow from the heat exchanger and to store the cool fluid flow for
re-cooling.
2. The subcooling circuit of claim 1, wherein the thermal storage
unit comprises: a first tank configured to supply the cool fluid
flow to the heat exchanger; and one or more second tanks fluidly
coupled to the first tank and configured to receive a warm fluid
flow from the heat exchanger, wherein the one or more second fluid
tanks are configured to cool the warm fluid into cool fluid, to
provide the cool fluid to the first tank, and to thermally isolate
the cool fluid in the first tank from the warm cooling fluid in the
one or more second tanks.
3. The subcooling circuit of claim 1, comprising: at least one
sensor configured to measure an operating parameter of the heat
exchanger; and a controller configured to regulate a flow rate of
the pump based at least partially on the operating parameter, and
the operating parameter comprises a temperature of the refrigerant
entering the heat exchanger, a temperature of the refrigerant
exiting the heat exchanger, a temperature of the cool fluid flow
entering the heat exchanger, a temperature of the cool fluid flow
exiting the heat exchanger, or a combination thereof.
4. The subcooling circuit of claim 1, wherein the cooling system
comprises a cooling heat exchanger configured to re-cool the cool
fluid flow in the thermal storage unit with the refrigerant.
5. The subcooling circuit of claim 1, wherein the thermal storage
unit comprises a stratified cooling fluid tank.
6. The subcooling circuit of claim 1, wherein the thermal storage
unit comprises a cooling fluid tank comprising a moveable partition
defining a first reservoir and a second reservoir of the cooling
fluid tank.
7. The subcooling circuit of claim 6, wherein the moveable
partition comprises: an insulation layer; a weight coupled to the
insulation layer; and a liner coupled to the insulation layer and
the cooling fluid tank, wherein the liner forms a watertight seal
between the first reservoir and the second reservoir.
8. The subcooling circuit of claim 1, wherein a flow rate of the
cool fluid flow is such that an increase in temperature of the cool
fluid flow across the heat exchanger is approximately equal to a
decrease in temperature of the refrigerant across the heat
exchanger.
9. The subcooling circuit of claim 1, wherein the cool fluid
comprises water.
10. A thermal storage system, comprising: a thermal storage unit
configured to store a cooling fluid; a first heat exchanger coupled
to the thermal storage unit; a first pump coupled to the thermal
storage unit and to the first heat exchanger, wherein the first
pump is configured to pump the cooling fluid through the first heat
exchanger in a recharge mode, and the thermal storage unit receives
the cooling fluid from the first heat exchanger after the cooling
fluid is cooled in the first heat exchanger in the recharge mode; a
second heat exchanger fluidly coupled to the thermal storage unit,
wherein the second heat exchanger is configured to receive a
refrigerant and the cooling fluid in a subcooling mode; and a
second pump coupled to the thermal storage unit and to the second
heat exchanger, wherein the second pump is configured to pump the
cooling fluid through the second heat exchanger in the subcooling
mode, and the thermal storage unit receives the cooling fluid from
the second heat exchanger after the cooling fluid is warmed by the
refrigerant in the second heat exchanger in the subcooling
mode.
11. The thermal storage system of claim 10, wherein the first heat
exchanger is configured to receive the cooling fluid and the
refrigerant in a recharge mode, the first heat exchanger is
configured to receive a load fluid and the refrigerant in the
subcooling mode, the refrigerant is configured to cool the cooling
fluid in the recharge mode, and the refrigerant is configured to
cool the load fluid in the subcooling mode, wherein the first pump
is configured to pump the load fluid through the first heat
exchanger in the subcooling mode.
12. The thermal storage system of claim 10, wherein during the
recharge mode the first pump is configured to pump the cooling
fluid through the first heat exchanger at a tank pressure of the
thermal storage unit, and during the subcooling mode the first pump
is configured to pump the load fluid through the first heat
exchanger at a load pressure different from the tank pressure.
13. The thermal storage system of claim 10, comprising an expansion
valve of a cooling circuit configured to circulate the refrigerant,
wherein the expansion valve is coupled between the first heat
exchanger and the second heat exchanger of the cooling circuit,
wherein the expansion valve is configured, in the subcooling mode,
to expand the refrigerant after the refrigerant is subcooled in the
second heat exchanger and before the refrigerant is received by the
first heat exchanger.
14. A method of utilizing a thermal storage unit with a refrigerant
circuit, comprising: cooling a refrigerant flow of the refrigerant
circuit with a cool water flow from the thermal storage unit to
generate a warm water flow and to cool the refrigerant flow by a
subcooling temperature difference; flowing the warm water flow to
the cool water storage; and thermally isolating the warm water flow
from the cool water flow in the cool water storage.
15. The method of claim 14, comprising regulating a flow rate of
the cool water flow such that a first temperature difference
between the cool water flow and the warm water flow is
approximately equal to the subcooling temperature difference.
16. The method of claim 15, wherein the first temperature
difference is greater than approximately 20.degree. Fahrenheit.
17. The method of claim 14, wherein thermally isolating the warm
water flow from the cool water flow comprises regulating a flow
rate of the warm water flow such that the warm water flow
stratifies above the cool water flow in the cool water storage.
18. The method of claim 14, wherein thermally isolating the warm
water flow from the cool water flow in the cool water storage
comprises storing the warm water flow in a first reservoir of the
cool water storage, and storing the cool water flow in a second
reservoir of the cool water storage, wherein the first and second
reservoirs are separated by a watertight, movable partition.
19. The method of claim 14, comprising cooling the warm water flow
of the cool water storage in a recharge mode with a cooling heat
exchanger disposed along the refrigerant circuit.
20. The method of claim 14, wherein thermally isolating the warm
water flow from the cool water flow in the cool water storage
comprises storing the warm water flow in a first tank of the cool
water storage and storing the cool water flow in a second tank of
the cool water storage, wherein the first and second tanks are
fluidly coupled.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 14/203,251 filed Mar. 10, 2014 , entitled
"SUBCOOLING SYSTEM WITH THERMAL STORAGE," which claims priority
from and the benefit of U.S. Provisional Application Ser. No.
61/793,632 , filed Mar. 15, 2013 , entitled "SUBCOOLING SYSTEM WITH
THERMAL STORAGE," both of which are hereby incorporated by
reference.
BACKGROUND
[0002] The present disclosure relates generally to cooling systems,
and more particularly, to subcooling systems for cooling
systems.
[0003] It has long been recognized that subcooling can improve both
efficiency and capacity of cooling systems (e.g., refrigeration
systems). Subcooling systems may include condensers, economizers,
flash tanks, heat exchangers, flash intercoolers, and/or
compressors (e.g., multi-stage compressors) for cooling condensed
refrigerant liquid before the condensed refrigerant liquid reaches
the evaporator of a cooling system. As the refrigerant is cooled,
enthalpy of refrigerant liquid flowing toward the evaporator is
reduced, thereby increasing cooling capacity with little or no
change to the work performed by the compressor. The result is
improved cooling system efficiency and capacity.
SUMMARY
[0004] The present invention relates to a system having a
refrigerant circuit configured to flow a refrigerant and a
subcooling circuit configured to flow a cooling fluid. The
refrigerant circuit includes a compressor, a condenser, an
expansion device configured to expand the refrigerant, a subcooling
heat exchanger, and a cooling heat exchanger. The subcooling
circuit includes the subcooling heat exchanger, a subcooling pump,
and a thermal storage unit configured to store the cooling
fluid.
[0005] The present invention also relates to a method that includes
cooling a refrigerant flow of a refrigerant circuit with a cool
water flow from a cool water storage to generate a warm water flow
and to cool the refrigerant flow by a subcooling temperature
difference, flowing the warm water flow to the cool water storage,
and thermally isolating the warm water flow from the cool water
flow in the cool water storage.
[0006] The present invention further relates to a subcooling
circuit having a thermal storage unit configured to store a cool
fluid, a heat exchanger configured to transfer heat between a cool
fluid flow of the thermal storage unit and a refrigerant of a
cooling system, and a pump configured to pump the cool fluid flow
through the subcooling circuit, wherein the thermal storage unit is
configured to receive the cool fluid flow from the heat exchanger
and to store the cool fluid flow for re-cooling.
DRAWINGS
[0007] FIG. 1 is a schematic of a cooling system having a
subcooling system, in accordance with embodiments of the present
disclosure;
[0008] FIG. 2 is a schematic of a cooling system having a
subcooling system with thermal storage including a stratified
cooling fluid tank, in accordance with embodiments of the present
disclosure;
[0009] FIG. 3 is a schematic of a cooling system having a
subcooling system with thermal storage including a stratified
cooling fluid tank, in accordance with embodiments of the present
disclosure;
[0010] FIG. 4 is a schematic of a cooling system having a
subcooling system with thermal storage including multiple cooling
fluid tanks, in accordance with embodiments of the present
disclosure;
[0011] FIG. 5 is a schematic of a cooling system having a
subcooling system with thermal storage including a cooling fluid
tank with a moveable partition, in accordance with embodiments of
the present disclosure;
[0012] FIG. 6 is a schematic side view of a thermal storage tank of
a subcooling system, in accordance with embodiments of the present
disclosure;
[0013] FIG. 7 is a schematic top view of a thermal storage tank of
a subcooling system, in accordance with embodiments of the present
disclosure;
[0014] FIG. 8 is a schematic side view of a roller of the thermal
storage tank of FIG. 6, in accordance with embodiments of the
present disclosure;
[0015] FIG. 9 is a schematic of a cooling system having a
subcooling system with thermal storage including a cooling fluid
tank with vertically arranged fluid connections, in accordance with
embodiments of the present disclosure;
[0016] FIG. 10 is a schematic of a cooling system having a
subcooling system with thermal storage including multiple cooling
fluid tanks arranged in series, in accordance with embodiments of
the present disclosure;
[0017] FIG. 11 is a schematic of a cooling system having a
subcooling system with thermal storage including multiple cooling
fluid tanks, in accordance with embodiments of the present
disclosure;
[0018] FIG. 12 is a schematic of a cooling system having a
subcooling system with thermal storage including multiple
subterranean fluid storage loops, in accordance with embodiments of
the present disclosure;
[0019] FIG. 13 is a schematic of a cooling system having a
subcooling system with thermal storage including a single pass
cooling fluid system, in accordance with embodiments of the present
disclosure;
[0020] FIG. 14 is a schematic of a cooling system having a
subcooling system with thermal storage including multiple coolers
and subcoolers arranged in parallel, in accordance with embodiments
of the present disclosure;
[0021] FIG. 15 is a schematic of a cooling system having a
subcooling system with thermal storage including two vertically
arranged cooling fluid tanks, in accordance with embodiments of the
present disclosure;
[0022] FIG. 16 is a pressure-enthalpy diagram for the cooling
system of FIG. 15, in accordance with embodiments of the present
disclosure;
[0023] FIG. 17 is a schematic of a cooling system having a
subcooling system with thermal storage including an ice storage
tank, in accordance with embodiments of the present disclosure;
and
[0024] FIG. 18 is a schematic of a cooling system having a
subcooling system with thermal storage tanks coupled in series, in
accordance with embodiments of the present disclosure.
DETAILED DESCRIPTION
[0025] Embodiments of the present disclosure are directed towards
improved subcooling systems for cooling systems (e.g.,
refrigeration systems). As will be appreciated, subcooling
increases cooling capacity of a cooling system by reducing the
enthalpy of refrigerant entering an evaporator (e.g., cooler) of
the cooling system. For example, energy removed from the
refrigerant liquid may correspond to an increase in cooling
capacity of the cooling system. As described in detail below, the
disclosed embodiments may include a cooling system with subcooling
system having a subcooling heat exchanger that uses a cooling fluid
(e.g., water, glycol solution, carbon dioxide, refrigerant) flow to
absorb heat from a refrigerant flow of the cooling system. In
particular, a flow rate of the cooling fluid flow through the heat
exchanger may be regulated to maximize the efficiency of the
subcooling system. For example, the cooling fluid flow rate may be
adjusted such that a temperature change of the cooling fluid flow
across the subcooling heat exchanger may be similar or equal to a
temperature change of the refrigerant across the subcooling heat
exchanger. Furthermore, in certain embodiments, the subcooling
system may include a thermal storage unit, such as a cooling fluid
tank, which may be a rechargeable source of the cooling fluid
flow.
[0026] Turning now to the drawings, FIG. 1 is a schematic of a
cooling system 10 having an improved subcooling system 12 in
accordance with present embodiments. The cooling system 10 may be
any suitable cooling system that supplies a chilled fluid to a load
14 and/or chills a fluid flow supplied to the load 14. For example,
the cooling system 10 may be a chiller, a room air conditioner, a
residential split-system air conditioner, or other type of
refrigeration system. As described in detail below, the cooling
system 10 may include a refrigerant circuit that chills a fluid
flow supplied to the load 14. Additionally, the subcooling system
12 may be configured to further cool the refrigerant flowing
through the refrigerant circuit of the cooling system 10 with a
subcooling fluid flow, thereby increasing the capacity of the
refrigerant to absorb heat. For example, in certain embodiments,
the subcooling system 12 may cool the refrigerant between a
condenser and an expansion valve of the refrigerant circuit. As may
be appreciated, the condenser and the expansion valve reduce the
temperature and the enthalpy of the refrigerant. As described
herein, the subcooling system 12 may further cool and decrease the
enthalpy of the refrigerant. The additional temperature and
enthalpy reduction from the subcooling system 12 may increase the
capacity of the cooling system for a particular amount of work,
such as the work of a compressor of the cooling system 10. For
example, the subcooling system 12 may increase the capacity of the
cooling system from approximately 7,000 kW with 2,500 kW input
power to approximately 9,000 kW with 2,500 kW input power.
Additionally, or in the alternative, the additional temperature and
enthalpy reduction from the subcooling system 12 may reduce the
amount of work (e.g., from 3,500 kW to 2,500 kW) to provide a
particular amount (e.g., 9,000 kW) of cooling. Furthermore, as
discussed below, the subcooling system 12 may include a thermal
storage unit, such as a cooling water tank, which may be
rechargeable. In this manner, efficiency of the subcooling system
12 and the cooling system 10 may be improved.
[0027] FIG. 2 is a schematic of an embodiment of the cooling system
10 having a refrigerant circuit 20 and the subcooling system 12.
For example, the cooling system 10 may be a water-cooled or
air-cooled chiller. As shown, the cooling system 10 includes the
refrigerant circuit 20 configured to cool a load fluid 22, which
includes fluid passing through a load circuit 23 portion of the
cooling system 10. The load fluid 22 may include, but is not
limited to, water, deionized water, glycol solution, carbon
dioxide, a refrigerant (e.g., R134a, R410A, R32, R1233ZD(E),
R1233zd (E), R1234yf, R1234ze), or any combination thereof. More
specifically, the refrigerant circuit 20 includes a cooler 24 in
which a refrigerant 25 may cool the load fluid 22. The cooler 24
may also be referred to herein as a cooling heat exchanger. The
refrigerant 25 may include, but is not limited to, carbon dioxide,
R134a, R410A, R32, R1233ZD(E), R1233zd (E), R1234yf, or R1234ze, or
another refrigerant as may be appreciated by one of skill in the
art. The refrigerant circuit 20 further includes a compressor 26
(e.g., centrifugal compressor, screw compressor, scroll compressor,
reciprocating compressor, or linear compressor), a condenser 28,
and an expansion device 30 (e.g., a fixed orifice, an electronic
expansion valve, a motorized butterfly valve, or a thermal
expansion valve).
[0028] The subcooling system 12 is thermally coupled to the
refrigerant circuit 20 to subcool the refrigerant 25. For example,
the subcooling system 12 may be coupled to the refrigerant circuit
20 via a subcooling heat exchanger 32 disposed along the
refrigerant circuit 20 between the condenser 28 and the expansion
device 30 (e.g., expansion valve). As such, the subcooling system
12 may flow a cooling fluid 33 (e.g., cool water) through a
subcooling circuit 34 and through the subcooling heat exchanger 32.
In some embodiments, the cooling fluid 33 may be substantially the
same fluid as the load fluid 22. Indeed, with respect to the
embodiments of FIG. 2, different names for the load fluid 22 and
cooling fluid 33 are utilized to facilitate communication of uses
of the fluid within the cooling system 10. Additionally, or in the
alternative, the cooling fluid may include, but is not limited to,
water, deionized water, glycol solution, carbon dioxide, a
refrigerant (e.g., R134a, R410A, R32, R1233ZD(E), R1233zd (E),
R1234yf, R1234ze), or any combination thereof. In this manner, heat
may be transferred from the refrigerant 25 of the refrigerant
circuit 20 to the cooling fluid 33 (e.g., cool water) of the
subcooling circuit 34 via the subcooling heat exchanger 32.
Additionally, a thermal storage unit 36 is disposed along the
subcooling circuit 34 of the subcooling system 12. For example, the
thermal storage unit 36 may be a stratified water tank configured
to store the cooling fluid 33 flowing through the subcooling system
12. The subcooling system 12 further includes a plurality of valves
(e.g., a first valve 38 between the load 14 and the chilled fluid
pump 48, a second valve 40 between the thermal storage unit 36 and
the chilled fluid pump 48, a third valve 42 between the cooler 24
(e.g., cooling heat exchanger) and the thermal storage unit 36, and
a fourth valve 44 between the subcooling heat exchanger 32 and the
thermal storage unit 36), which may be operated to regulate the
cooling fluid 33 flowing through the subcooling circuit 34. As the
flow of the cooling fluid 33 is regulated by the valves 38, 40, 42,
and 44, heat transfer between the cooling fluid 33 of the
subcooling system 12 and the refrigerant 25 of the cooling system
10 may be regulated. In certain embodiments, the subcooling system
12 may have different modes of operation based on which of the
valves 38, 40, 42, and 44 are opened, and which of the valves 38,
40, 42, and 44 are closed.
[0029] For example, when the first valve 38 is configured to allow
the load fluid 22 to flow from the load 14 to the chilled fluid
pump 48, the third valve 42 is closed, and the second valve 40 and
the fourth valve 44 are open, the subcooling system 12 may be in a
subcooling mode. In the subcooling mode, at least a portion (e.g.,
approximately 5 to 20 percent) of the load fluid 22 (e.g., return
water 45, cold chilled fluid 33) may flow from the chilled fluid
pump 48 through the subcooling heat exchanger 32, as indicated by
arrow 46, to a top 47 of the thermal storage unit 36 (e.g.,
stratified water tank). The remainder of the load fluid 22 from the
chilled fluid pump 48 may flow through the cooler 24 (e.g., cooling
heat exchanger). As will be appreciated, within the thermal storage
unit 36, a temperature gradient may exist across the cooling fluid
33 within the thermal storage unit 36. More specifically, the
temperature of the cooling fluid 33 (e.g., water) at a bottom 49 of
the thermal storage unit 36 may be lower than the temperature of
the cooling fluid 33 at the top 47 of the thermal storage unit 36.
As such, cold cooling fluid 33 from the bottom 49 of the thermal
storage unit 36 may flow into and join the return water 45 flow
upstream of the chilled fluid pump 48. The addition of the cold
cooling fluid 33 from the thermal storage unit 36 enables the
cooling fluid 33 through the subcooling heat exchanger 32 to be at
a lower temperature than the return water 45.
[0030] As mentioned above, the flow rate of the cooling fluid 33
(e.g., return water 45 and cold cooling fluid 33 from the thermal
storage unit 36) flowing through the subcooling circuit 34 may be
regulated to achieve a desired temperature drop of the refrigerant
25 across the subcooling heat exchanger 32. More specifically, the
valves 38, 40, 42, and 44 may be regulated such that a temperature
difference (e.g., increase) of the cooling fluid 33 across the
subcooling heat exchanger 32 is approximately equal to the
temperature difference (e.g., decrease) of the refrigerant 25
across the subcooling heat exchanger 32. The result is that the
temperature of the refrigerant 25 (e.g., liquid refrigerant) may
approach the temperature (e.g., between approximately 32 to
50.degree. F.) of the cooling fluid 33 entering the subcooling heat
exchanger 32, and the temperature of the cooling fluid 33 may
approach the temperature (e.g., approximately 60, 80, 100, 120,
140.degree. F.) of the refrigerant 25 leaving the condenser 28. The
expansion device 30 receiving the refrigerant 25 downstream of the
subcooling heat exchanger 32 reduces the pressure and the
temperature of the refrigerant 25, thereby enabling the refrigerant
25 to cool the load fluid 22 via the cooler 24 (e.g., cooling heat
exchanger). For example, the change (e.g., increase) in temperature
of the cooling fluid 33 may be approximately 40 to 80.degree. F.
across the subcooling heat exchanger 32, and the change (e.g.,
decrease) in temperature of the refrigerant 25 may be approximately
40 to 80.degree. F. across the subcooling heat exchanger 32. As a
result, the energy storage capacity of the thermal storage unit 36
may be much greater than that of conventional chilled water storage
systems.
[0031] In some embodiments, the flows of the refrigerant 25 and the
cooling fluid 33 through the subcooling heat exchanger 32 may
approximate a counterflow configuration. For example, multi-pass
brazed-plate heat exchangers, such as those available by SWEP of
Landskrona, Sweden, may be utilized. Multi-pass brazed-plate may
have a substantially compact profile and/or footprint, and may
efficiently transfer heat between fluids. In some embodiments, the
temperature difference between the refrigerant 25 exiting the
subcooling heat exchanger 32 and the cooling fluid 33 entering the
subcooling heat exchanger 32 may be less than approximately 10, 8,
5, or 2 degrees Fahrenheit. In some embodiments, the temperature
difference may correspond to an effectiveness of the subcooling
heat exchanger greater than approximately 90, 91, 92, 93, 94, or 95
percent. The flow rate of the cooling fluid 33 through the
subcooling heat exchanger 32 relative to the flow rate of the
refrigerant 25 may be adjustable, thereby enabling the control of
the temperature difference between the exiting refrigerant 25 and
the entering cooling fluid 33. In some embodiments, the relative
flow rate of the cooling fluid 33 may be adjusted based on a
desired cooling capacity of the cooling system 10, a thermal
storage capacity of the thermal storage unit 36, or any combination
thereof. For example, the relative flow rate of the cooling fluid
33 may be decreased, thereby reducing the temperature difference
between the exiting refrigerant 25 and the entering cooling fluid
33, to increase the cooling capacity of the cooling system.
Alternatively, the relative flow rate of the cooling fluid 33 may
be increased, thereby increasing the temperature difference between
the exiting refrigerant 25 and the entering cooling fluid 33, to
decrease the thermal energy transferred from the thermal storage
unit 36 to the refrigerant 25.
[0032] In some embodiments, the subcooling system 12 may be at
least partially disposed in an environment subject to temperatures
near or below freezing (e.g., 32.degree. F.). The subcooling system
12 may include thermal insulation about portions of the subcooling
circuit 34, heaters (e.g., gas heaters, electric heaters), or any
combination thereof. Additionally or in the alternative, the
cooling fluid 33 of the subcooling system 12 may be mixed with
propylene, ethylene glycol, or an antifreeze, thereby lowering the
freezing point of the cooling fluid 33 below an expected freezing
environment temperature. In some embodiments, a valve 51 (e.g.,
solenoid valve) in the refrigerant circuit 20 disposed between the
condenser 28 and the subcooling heat exchanger 32 may close to
prevent a thermosiphon when the refrigerant circuit 20 is not
circulating the refrigerant 25.
[0033] To achieve the desired temperature gradients across the
subcooling heat exchanger 32, the cooling system 10 may include one
or more sensors 50 on the refrigerant circuit 20 and/or the
subcooling system 12. Each of the one or more sensors 50 is
configured to measure one or more operating parameters (e.g.,
temperature, pressure, etc.) of the refrigerant 25 and/or the
cooling fluid 33. The sensors 50 may provide measured feedback to a
controller 52 (e.g., an automation controller, programmable logic
controller, distributed control system, etc.) by a wireless (e.g.,
via an antenna 53) or hard wired connection. In certain
embodiments, the controller 52 may be further configured to
regulate (e.g., automatically) operation of one or more of the
valves 38, 40, 42, and 44 in response to feedback measured by the
sensors 50. In other embodiments, the valves 38, 40, 42, and 44 may
be operated manually. Additionally, other processes of the cooling
system 10 may be controlled by the controller 52 by a wireless
(e.g., via the antenna 53) or hard wired connection.
[0034] In a recharge mode of the subcooling system 12, the second
and fourth valves 40 and 44 are closed, while the first valve 38
and third valve 42 are opened to allow the flow indicated by arrows
54. As a result, during operation in the recharge mode, the cooling
fluid 33 (e.g., water) flows through the subcooling circuit 34, as
indicated by arrows 54. More specifically, warm cooling fluid 33
from the top 47 of the thermal storage unit 36 flows through the
cooling system 10, causing the cooling fluid 33 to decrease in
temperature. Thereafter, the cooling fluid 33 is returned to the
bottom 49 of the thermal storage unit 36. As a result, the cooling
fluid 33 within the thermal storage unit 36 may gradually decrease
in temperature, thereby "recharging" the thermal storage unit
36.
[0035] Flow rate of the cooling fluid 33 (e.g., water) through the
thermal storage unit (e.g., tank) 36 may be much higher during
recharge mode than during subcooling mode. As shown in FIG. 2, the
full flow of the chilled fluid pump 48 would be directed through
the thermal storage unit 36 during recharge mode when the fourth
valve 44 is closed, while only a small fraction of the flow
(between approximately 5 to 20 percent) would be directed through
the thermal storage unit 36 (e.g., through the second valve 40) in
subcooling mode when the fourth valve 44 is open. This difference
in flow rates between the recharge mode and the subcooling mode
means that stratified conditions within the thermal storage unit 36
(e.g., stratified water tank) are relatively easy to maintain in
subcooling mode, but mixing may occur during recharge.
[0036] In certain embodiments, the thermal storage unit 36 (e.g.,
stratified water tank) may include piping configured to minimize
mixing of cooling fluid 33 entering the thermal storage unit 36.
For example, the diameter of the piping, the arrangement of the
piping into the thermal storage unit 36, and a flow rate of the
cooling fluid 33 through the piping may reduce mixing of the
cooling fluid within the thermal storage unit 36, thereby enabling
stratification of the cooling fluid 33. As may be appreciated, the
density of the cooling fluid 33 is based at least in part on the
temperature of the cooling fluid 33. For example, the density of
water generally decreases as the temperature increases.
Accordingly, a relatively large difference (e.g., greater than 10,
20, 30, 40, or 50.degree. F.) in temperature between the cold
cooling fluid 33 in the thermal storage unit 36 and the warm
cooling fluid 33 returning from the subcooling heat exchanger 32
may enable the warm cooling fluid to readily stratify above the
cold cooling fluid. In other embodiments, the thermal storage unit
36 may include piping to mix entering cooling fluid 33 (e.g., warm
water) with cooling fluid 33 (e.g., cold water) at the bottom 49 of
the thermal storage unit 36. Furthermore, in certain environments,
the thermal storage unit 36 may be designed to have walls to
withstand elevated environmental pressures. It may be desirable for
the exterior of the thermal storage unit 36 to include thermal
insulation to reduce heat transfer to the environment. The
insulation may be placed on the inside or the outside of the walls
of the thermal storage unit 36.
[0037] FIG. 3 is a schematic of an embodiment of the cooling system
10 having the refrigerant circuit 20 and the subcooling system 12.
Specifically, the illustrated embodiment of the cooling system 10
allows for a pressure difference between the thermal storage unit
36 of the subcooling system 12 and the refrigerant circuit 20.
Additionally, the illustrated embodiment has similar elements and
element numbers as the embodiment shown in FIG. 2.
[0038] As similarly described above, the cooling system 10 has the
first, second, third, and fourth valves 38, 40, 42, and 44 to
control the flow of the load fluid 22 and the cooling fluid 33
through the cooler 24 (e.g., cooling heat exchanger) and subcooling
heat exchanger 32. For example, the first, second, third, and
fourth valves 38, 40, 42, and 44 may be low-leakage valves, such as
ball valves. The first valve 38 is between the cooler 24 (e.g.,
cooling heat exchanger) and the load 14, the second valve 40 is
between the cooler 24 (e.g., cooling heat exchanger) and the
thermal storage unit 36, the third valve 42 is between the thermal
storage unit 36 and the chilled fluid pump 48, and the fourth valve
is between the load 14 and the chilled fluid pump 48. Moreover, in
addition to the chilled fluid pump 48, the illustrated embodiment
includes a subcooling pump 100 configured to pump the cooling fluid
33 through the subcooling circuit 34, which may be at a different
pressure than the load fluid 22 fluidly coupled to the load 14. The
first, second, third, and fourth valves 38, 40, 42, and 44 and the
pumps 48 and 100 may be regulated or controlled (e.g., via a
control system including the automation controller 52) to enable
operation of the cooling system 10 and subcooling system 12 in
different modes.
[0039] For example, the first and second valves 38 and 40 control
flow of the chilled fluid (e.g., load fluid 22, cooling fluid 33)
leaving the cooler 24 (e.g., cooling heat exchanger). Specifically,
the first valve 38 controls the flow of chilled load fluid 22 to
the load 14 (e.g., a building chilled water loop) during the
subcooling mode. Additionally, the second valve 40 controls the
flow of chilled cooling fluid 33 from the cooler 24 (e.g., cooling
heat exchanger) to the bottom 49 of the thermal storage unit 36
(e.g., stratified water tank) during the recharge mode. As further
shown, the third and fourth valves 42 and 44 are disposed on the
suction side of the chilled fluid pump 48. Specifically, the third
valve 42 regulates flow of the cooling fluid 33 from the top 47 of
the thermal storage unit 36 to the chilled fluid pump 48 during the
recharge mode, and the fourth valve 44 controls flow of the load
fluid 22 (e.g., return water 45) returning from the load 14 to the
chilled fluid pump 48 during the subcooling mode.
[0040] Furthermore, the subcooling pump 100 draws the cooling fluid
33 from the bottom 49 of the thermal storage unit 36 and pumps the
cooling fluid 33 from the thermal storage unit 36 through the
subcooling heat exchanger 32 to subcool the refrigerant 25 of the
refrigerant circuit 20. After passing through the subcooling heat
exchanger 32, the cooling fluid 33 flows to the top 47 of the
thermal storage unit 36. As described above, the cooling fluid 33
flowing through the subcooling heat exchanger 32 absorbs heat from
the refrigerant 25 flowing through the refrigerant circuit 20 of
the cooling system 10 via the subcooling heat exchanger 32 (e.g.,
subcooler). In certain embodiments, the flow rate of cooling fluid
33 through the subcooling pump 100 and subcooling heat exchanger 32
may be much lower than the flow rate of fluid (e.g., load fluid 22,
cooling fluid 33) through the chilled fluid pump 48. For example,
the chilled fluid pump 48 may pump a fluid (e.g., load fluid 22,
cooling fluid 33) at approximately 10 to 20 times the rate that the
subcooling pump 100 pumps the cooling fluid 33. In some
embodiments, the subcooling pump 100 may pump the chilled fluid 33
at a flow rate that enables the temperature of the cooling fluid 33
exiting the subcooling heat exchanger 32 to be less than 5, 4, 3,
2, or 1.degree. Fahrenheit of the temperature of the refrigerant 25
entering the subcooling heat exchanger 32. The subcooling pump 100
may be a variable speed circulator pump, as may be available by
Taco of Cranston, R.I. As may be appreciated, decreasing the
temperature difference between the exiting cooling fluid 33 and the
entering refrigerant 25 via control of the subcooling pump 100 may
increase the efficiency of the cooling system 10. Moreover, in some
embodiments, the subcooling pump 100 may pump the chilled fluid 33
through the subcooling heat exchanger 32 at a flow rate less than
the flow rate of the refrigerant 25 through the subcooling heat
exchanger 32. For example, the flow of the chilled fluid 33 through
the subcooling heat exchanger 32 may be approximately 5, 10, 20,
30, 40, 50 of the flow rate of the refrigerant 25 through the
subcooling heat exchanger 32. The flow rate of the chilled fluid 33
through the subcooling heat exchanger 32 relative to the flow rate
of the refrigerant 25 through the subcooling heat exchanger 32 may
be variable, based at least in part on a desired cooling capacity
of the cooling system.
[0041] During a subcooling mode of the illustrated embodiment in
FIG. 3, the chilled fluid pump 48 and the subcooling pump 100 may
both be running. Additionally, the first and fourth valves 38 and
44 are open, while the second and third valves 40 and 42 are
closed. In such a configuration, the cooler 24 (e.g., cooling heat
exchanger) and the chilled fluid pump 48 are coupled to the load
14, while being isolated from the thermal storage unit 36.
Moreover, in such a configuration, the subcooling pump 100
circulates cooling fluid 33 (e.g., water) from the bottom 49 of the
thermal storage unit 36, through the subcooling heat exchanger 32,
and back to the top 47 of the thermal storage unit 36, as indicated
by arrows 102. In this manner, the cooling fluid 33 in the thermal
storage unit 36 (e.g., stratified water tank) cools the refrigerant
25 of the cooling system 10 via the subcooling heat exchanger 32,
thereby increasing the cooling capacity of the cooling system 10.
As will be appreciated, the cooling system 10 may be in the
subcooling configuration or subcooling mode (e.g., first and fourth
valves 38, 44 open, second and third valves 40, 42 closed) during
times of peak electrical prices and peak cooling load. For example,
the illustrated embodiment may be in the subcooling configuration
during the daytime and/or during the evening in warm weather.
[0042] To enter the recharging mode from the subcooling mode, the
chilled fluid pump 48 and the subcooling pump 100 may both be
turned off. Additionally, the first and fourth valves 38 and 44 are
closed. In this manner, the cooler 24 (e.g., cooling heat
exchanger) and the chilled fluid pump 48 may be isolated from the
load 14. Once the first and fourth valves 38 and 44 are closed, the
second and third valves 40 and 42 are opened to connect the cooler
24 (e.g., cooling heat exchanger) and the chilled fluid pump 48 to
the thermal storage unit 36.
[0043] In some embodiments, the flow rate of the cooling fluid 33
may be increased during the recharge mode relative to the
subcooling mode such that the chilled fluid 33 within the thermal
storage unit 36 is mixed. With the second and third valves 40 and
42 opened, the chilled fluid pump 48 may be turned on to pump
cooling fluid 33 (e.g., water) through the cooler 24 (e.g., cooling
heat exchanger) as shown by arrows 54. As a result, the cooling
fluid 33 (e.g., water) within the thermal storage unit 36 may be
cooled, thereby "recharging" the cooling capacity of the thermal
storage unit 36. As similarly discussed above, the cooling system
10 and subcooling system 12 may be in the recharging mode when
energy rates are lower (e.g., night time).
[0044] In order to revert back to the subcooling mode from the
recharging mode, the chilled fluid pump 48 is once again turned
off, the second and third valves 40 and 42 are closed, and the
first and fourth valves 38 and 44 are opened. Thereafter, the
chilled fluid pump 48 and the subcooling pump 100 may both be
turned on, and the cooling fluid 33 in the thermal storage unit 36
may be circulated as shown by arrows 102 to cool the refrigerant 25
in the manner described above.
[0045] A feature of this embodiment of the cooling system 10 is
that it allows for a pressure difference between portions of the
cooling system 10, such as between the thermal storage unit 36 and
the load circuit 23 supplying the load 14, if valves 38, 40, 42,
and 44 can provide positive shut off. Examples of valves that can
provide pressure isolation include butterfly valves or ball valves.
It may be desirable for the valves to be motor-actuated to allow
for automatic control of the system. Additionally, or in the
alternative, manual valves may be utilized for pressure isoliation.
This pressure isolation feature may be particularly desirable in
multistory buildings wherein the thermal storage unit 36 is located
at ground level. In subcooling mode, valves 40 and 42 are closed,
which isolates the thermal storage unit 36 from the pressure of the
load circuit 23 (e.g., building loop). The chilled fluid pump 48
may direct the load fluid 22 through the cooler 24 at the pressure
of the load circuit 23. In recharge mode, valves 38 and 44 are
closed. The chilled fluid pump 48 may direct the cooling fluid 33
through the cooler 24 at a tank pressure (e.g., the pressure of the
thermal storage unit 36) different from the pressure of the load
circuit 23. Interlocks (e.g., control logic of an automation
controller) can be provided to ensure that neither the second valve
40 nor the third 42 is open whenever either the first valve 38 or
the fourth valve 44 is open. It may also be desirable to include
space in the thermal storage unit 36 to handle the full system
fluid volume (e.g., load fluid 22 and cooling fluid 33) without
overflowing in case of a leaking valve (e.g., second valve 40,
third valve 42). The pressure-isolation characteristics of present
embodiments may eliminate or limit the cost and performance
penalties that typically accompany other options (e.g., a
water-to-water heat exchanger, a high-pressure water storage tank,
or a support structure required to locate the tank physically
higher). Present embodiments facilitate packaging of components to
simplify installation in the field. For example all the pumps and
valves can be packaged with the subcooling system 12 in a single
unit, which eliminates field piping and wiring and allows the
controls of the pumps and valves to be integrated into a chiller
control (e.g., automation controller). In addition, the subcooling
circuit 34 and a recharge conduit 35 may connect through a tee 104
to a single pipe 106 to the top 47 of the thermal storage unit 36.
Similarly, a single pipe 108 communicatively coupled to the bottom
49 of the thermal storage unit 36 can be provided. This setup means
that only four fluid (e.g., water) connections are performed at
installation. These could be load connections 110 for supply and
return of the load fluid 22 with the load 14 and tank connections
112 to the top 47 and the bottom 49 of the thermal storage unit 36.
The piping for the thermal storage unit 36 may be inexpensive
(e.g., plastic) pipe in embodiments with only a low fluid
pressure.
[0046] FIG. 4 is an embodiment of the cooling system 10 having the
refrigerant circuit 20 and the subcooling system 12, where the
subcooling system 12 has multiple thermal storage units 36. More
specifically, the illustrated embodiment includes two thermal
storage units 36 (e.g., stratified water tanks) and associated
valves 120 so that one thermal storage unit 36 can recharge while
the other thermal storage unit 36 is supplying the cooling fluid 33
to the one or more subcooling heat exchangers 32. In this manner,
the thermal storage units 36 can be continually recharged
throughout the day. Furthermore, the illustrated embodiment reduces
the size of each thermal storage unit 36, and may increase
efficiency of the subcooling system 12. For example, the valves 120
may be controlled so that the cooling fluid 33 is drawn from a
first thermal storage unit 122 until the average temperature of the
cooling fluid 33 of the first thermal storage unit 122 reaches a
subcooler threshold temperature (e.g., temperature of the load
fluid 22). Then, the cooling fluid 33 may be drawn from a second
thermal storage unit 124 while the cooling fluid 33 of the first
thermal storage unit 122 recharges (e.g., cools) via the cooler 24.
The valves 120 illustrated in FIG. 4 may include the first, second,
third, and fourth valves 38, 40, 42, and 44 described above. The
first valve 38 is between the cooler 24 and the load 14, each
second valve 40 is between the cooler 24 and a respective thermal
storage unit 36, each third valve 42 is between a respective
thermal storage unit 36 and the chilled fluid pump 48, and the
fourth valve is between the load 14 and the chilled fluid pump
48.
[0047] FIG. 5 is a schematic of an embodiment of the cooling system
10 having at least one refrigerant circuit 20 and the subcooling
system 12, wherein the subcooling system 12 includes a stratified
fluid tank 138 as the thermal storage unit 36. Specifically, the
illustrated embodiment includes two subcooling loops 140 that share
the common stratified fluid tank 138. Additionally, the stratified
fluid tank 138 includes a moveable partition 142 to separate cold
cooling fluid 144 (e.g., cold water) from warm cooling fluid 146
(e.g., warm water) within the thermal storage unit 36. When the
subcooling system 12 is configured in the subcooling mode, both
subcooling pumps 100 (e.g., a first pump 148 and a second pump 150)
may operate to move the cold cooling fluid 144 from the bottom 49
of the stratified fluid tank 138 through each of the subcooling
heat exchangers 32 (e.g., a first subcooling heat exchanger 152 and
a second subcooling heat exchanger 154). In some embodiments, each
subcooling heat exchanger 32 may be fluidly coupled to a separate
refrigerant circuit 20 (e.g., first refrigerant circuit, second
refrigerant circuit). Alternatively, one or more of the subcooling
heat exchangers may be fluidly coupled to a common refrigerant
circuit 20, as illustrated in FIG. 4. The subcooling heat
exchangers 32 may be coupled to the same or a different refrigerant
circuit 20 relative to the refrigerant circuit 20 with the cooler
24 that recharges (e.g., cool) the cooling fluid 33.
[0048] When the subcooling system 12 is configured in the recharge
mode, a chilled fluid pump 156 may circulate the warm cooling fluid
146 from the top 47 of the stratified fluid tank 138 through the
cooler 24, which is part of a refrigerant circuit 20 (e.g., first
refrigerant circuit) of the cooling system 10, as described above.
The cooling fluid 33 (e.g., water) exiting the cooler 24 is
directed to two valves (e.g., a second valve 40A and a second valve
40B). As shown, the second valve 40A directs the cooling fluid 33
to the top 47 of the stratified fluid tank 138 from the cooler 24,
and the second valve 40B directs the cooling fluid 33 to the bottom
49 of the stratified fluid tank 138 from the cooler 24. At the
beginning of the recharge mode, the second valve 40A is opened and
the second valve 40B is closed so that the warm cooling fluid 146
(e.g., warm water) above the partition 142 is cooled first. Once
the stratified fluid tank 138 is cooled to the point where the
temperature of the cooling fluid 33 (e.g., warm cooling fluid 146)
leaving the stratified fluid tank 138 (e.g., out of the top 47 of
the stratified fluid tank 138) is near a predetermined value, the
second valve 40B is opened to allow cooling fluid 33 (e.g., cold
cooling fluid 144) into the bottom 49 of the stratified fluid tank
138 below the partition 142. The second valve 40A and the second
valve 40B may be controlled by a programmed automation controller
52, as is the case for other control schemes and processes
described herein. Moreover, as described above with FIG. 2, one or
more sensors 50 configured to measure operating parameters of the
cooling fluid 33 may provide feedback to the controller 52. The
controller 52 may utilize the feedback to control the first and
second valves 160. When the second valve 40B is opened, the second
valve 40A may be closed, which causes the cooling fluid 33 (e.g.,
warm cooling fluid 146) at the top 47 of the stratified fluid tank
138 to be drained, and the stratified fluid tank 138 to fill with
cold cooling fluid 144 at the bottom 49 of the stratified fluid
tank 138. Once the stratified fluid tank 138 is filled with cold
cooling fluid 144 below the partition 142, the cooler 24 may be
shut down as the stratified fluid tank 138 is recharged. The cooler
24 may not be shut down if the cooler 24 is otherwise coupled to a
refrigerant circuit 20 configured to cool a load 14.
[0049] In certain embodiments, the subcooling system 12 may include
a free-cooling heat exchanger. As will be appreciated, in certain
environments, such as deserts, ambient air temperatures may be
sufficiently low to enable air cooling of the cooling fluid 33
within the thermal storage unit 36 via a free-cooling heat
exchanger 162. The free-cooling heat exchanger 162 may be located
in addition to or in place of the cooler 24 between the chilled
fluid pump 156 and the first and second valves 158, 160. As such,
the cooling fluid 33 may be further cooled by ambient air before it
enters the cooler 24. Additionally or in the alternative, the same
or a different free-cooling heat exchanger 162 may be located in
the one or more subcooling loops 140 with the subcooling heat
exchangers 152 and 154. In such a configuration, one or more valves
164 may enable pumps 148 and 150 to draw cooling fluid 33 (e.g.,
warm cooling fluid 146) from the top 47 of the thermal storage unit
36 through the free-cooling heat exchanger 162. Furthermore, a
free-cooling heat exchanger 162 may be located in a separate loop
with its own pump 166. In such an embodiment, the connections of
the separate loop may be positioned near the top 47 of the thermal
storage unit 36 so that the separate free-cooling loop cools the
warmest fluid (e.g., warm cooling fluid 146) from the thermal
storage unit 36.
[0050] FIGS. 6-8 are schematic representations of the thermal
storage unit 36 (e.g., stratified fluid tank 138) shown in FIG. 5.
For example, FIG. 6 is a side cross-sectional view of the
stratified fluid tank 138. Specifically, the illustrated stratified
fluid tank 138 is a cylindrical tank having the moveable partition
142 that separates cold cooling fluid 144 and warm cooling fluid
146. The moveable partition 142 may include a thermal insulation
layer 180 with a weight 182. As will be appreciated, the weight 182
may give the thermal insulation layer 180 a slightly negative
buoyancy relative to the cooling fluid 33. As discussed herein,
portions of the cooling fluid 33 may be identified by relative
temperature, where a cold cooling fluid 144 has a lower temperature
than a warm cooling fluid 146. As may be appreciated, the
stratified fluid tank 138 separates the cold cooling fluid 144 from
the warm cooling fluid 146. The cold cooling fluid 144 may be
utilized with one or more subcooling heat exchangers 32 to subcool
a refrigerant 25, where the cooling fluid 33 enters the subcooling
heat exchanger 32 as the cold cooling fluid 144 and exits the
subcooling heat exchanger 32 as the warm cooling fluid 146. The
warm cooling fluid 146 may be cooled during the recharge mode by
circulation through the cooler 24 or free-cooling heat exchanger
162, thereby returning the cooling fluid 33 to the thermal storage
unit 36 (e.g., stratified fluid tank 138) as cold cooling fluid
144.
[0051] The stratified fluid tank 138 further includes a liner 184.
More specifically, the liner 184 is an elastic, flexible, and
watertight liner 184 that is coupled to the moveable partition 142
and extends upward to the top 47 of the stratified fluid tank 138.
The liner 184 is attached to the top 47, to a wall 185 of the
stratified fluid tank 138, or to a float. Additionally, the liner
184 has two layers 186 that are rolled up and coupled to one
another (e.g., in a toroidal roll 188). For example, one layer 186
may form a flexible tube that is attached to the inside of the
stratified fluid tank 138 near the top 47 of the stratified fluid
tank 138. The other layer 186 forms another flexible tube that is
attached to the circumference of the moveable partition 142 (e.g.,
thermal insulation layer 180).
[0052] FIG. 7 is a top view of the stratified fluid tank 138 of
FIG. 5. As shown, the thermal insulation layer 180, the liner 184,
and an outer wall 200 of the stratified fluid tank 138 may be
generally concentric. Furthermore, FIG. 8 illustrates a
cross-sectional view of the toroidal roll 188 formed by the two
layers 186 of the liner 184, taken along line 8-8 of FIG. 6. As
indicated by arrow 210, each layer 186 of the liner 184 may be in
tension. That is, the thermal insulation layer 180 and the weight
182 may apply a tension force on the liner 184. In certain
embodiments, the thickness of the liner 184, the diameter of the
toroidal roll 188, the diameter of the thermal storage unit 36,
and/or the size of the weight 182 may be selected to achieve a
desired tension in the liner 184. As may be appreciated, the
stratified fluid tank 138 is not limited to a cylindrical tank. In
some embodiments, the stratified fluid tank 138 may have other
cross-sectional shapes, such as an ellipse, rectangle, pentagon,
hexagon, or another shape.
[0053] As mentioned above, the illustrated moveable partition 142
creates a fluid-sealed boundary between the cold cooling fluid 144
and the warm cooling fluid 146 within the stratified fluid tank
138. As will be appreciated, such a design may improve control of
the partition 142 position. For example, while the weight 182
provides a slightly negative buoyancy on the moveable partition
142, the curl (e.g., the spring force that acts to roll up the
toroidal roll 188) of the liner 184 may balance the negative
buoyancy caused by the weight 182 when the levels of cold cooling
fluid 144 and the warm cooling fluid 146 are approximately equal
within the stratified fluid tank 138. Furthermore, in such
circumstances, the tension on both sides of the liner 184 may be at
equilibrium, such that the moveable partition 142 is relatively
stationary. As cooling fluid 33 (e.g., water) is pumped into one
side of the thermal storage unit 36 (e.g., the cold cooling fluid
144 side or the warm cooling fluid 146 side), the moveable
partition 142 may move in response until approximately equal
tension is re-established. The result is that the moveable
partition 142 naturally seeks an equilibrium position without any
special controls.
[0054] In certain embodiments, the illustrated configuration may be
applicable to the storage of other liquids, such as gasses,
slurries, and other fluid materials in one or more thermal storage
units 36. Furthermore, while the embodiment illustrated in FIGS.
6-8 shows one moveable partition 142, other embodiments of the
thermal storage unit 36 may have other numbers of moveable
partitions 142 within a single tank. For example, the thermal
storage unit 36 may include an upper partition and a lower
partition. In such an embodiment, the upper partition may have a
smaller diameter than the lower partition, and an upper liner for
the upper partition may be positioned inside of a lower liner for
the lower partition. As a result, the thermal storage unit 36 may
have three separate layers or reservoirs of cooling fluid 33. That
is, a first reservoir of cooling fluid 33 (e.g., warm water exiting
the subcooling heat exchanger 32 at a temperature greater than
approximately 60.degree. F.) may be above the upper partition, a
second reservoir of cooling fluid 33 (e.g., water at an
intermediate temperature between approximately the temperature of
the warm water in the first reservoir and the temperature of the
cold water in the third reservoir) may be between the upper and
lower partitions, and a third reservoir of cooling fluid 33 (e.g.,
cold water at a temperature between approximately 32 to 50.degree.
F.) may be below the lower partition. The temperature of the warm
water exiting the subcooling heat exchanger 32 may be approximately
the temperature of the refrigerant 25 exiting the condenser 28 or a
maximum design temperature of the conduit carrying the warm water,
whichever is lower. Furthermore, other embodiments of the thermal
storage unit 36 may have more than two partitions.
[0055] FIG. 9 is a schematic of an embodiment of the cooling system
10 having at least one refrigerant circuit 20 and the subcooling
system 12, where the thermal storage unit 36 includes multiple
fluid connections 220 arranged vertically across the thermal
storage unit 36 (e.g., stratified fluid tank 138). The vertically
arranged fluid connections 220 enable only the cooling fluid 33
(e.g., warm water) near the top 47 of the thermal storage unit 36
to be cooled by the cooling fluid 33 that has been recharged (e.g.,
cooled) by the cooler 24, leaving the cooling fluid 33 (e.g., cold
water) at the bottom 49 of the thermal storage unit 36 relatively
undisturbed during a recharging mode. The controller 52 may control
(e.g., open, close) height valves 222 to inject cooling fluid 33
from the cooler 24 to one or more heights at a top portion 224
where the warm cooling fluid 146 is approximately stratified in the
thermal storage unit 36. Once the cooling fluid 33 at the top
portion 224 of the thermal storage unit 36 is cooled down to a
threshold temperature, cooling fluid 33 (e.g., cold water) from the
cooler 24 may be directed to the bottom 49 of the thermal storage
unit 36 through a bottom valve 226. As may be appreciated, the
cooling system 10 of FIG. 9 may have a similar arrangement of the
first, second, third, and fourth valves 38, 40, 42, and 44 as
described above with FIG. 3. The first valve 38 is between the
cooler 24 and the load 14, the second valve 40 is between the
cooler 24 and the thermal storage unit 36, the third valve 42 is
between the thermal storage unit 36 and the chilled fluid pump 48,
and the fourth valve is between the load 14 and the chilled fluid
pump 48.
[0056] FIG. 10 is a schematic of the cooling system 10 having the
refrigerant circuit 20 and the subcooling system 12, where the
subcooling system 12 includes multiple thermal storage units 36
coupled in series. During a subcooling (e.g., discharge) mode,
subcooling pumps 100 circulate cooling fluid 33 from one or more
thermal storage units 36 through one or more subcooling heat
exchangers 32 of one or more refrigerant circuits 20 to the top 47
of a first thermal storage unit 240 (e.g., a first tank). The
cooling fluid 33 may be cold cooling fluid 144 upon entering the
subcooling heat exchangers 32, and may exit as warm cooling fluid
146 upon absorbing heat from the refrigerant 25 of the one or more
refrigerant circuits 20. In some embodiments, the first, second,
and third thermal storage units 240, 242, and 244 may begin
operation each substantially filled with cold cooling fluid 144.
During the subcooling mode, cold cooling fluid 144 flows from the
third thermal storage unit 244 to the one or more subcooling heat
exchangers 32, and returns to the first thermal storage unit 240 as
warm cooling fluid 146. As may be appreciated, cooling fluid 33
(e.g., cold cooling fluid 144) flows from the second thermal
storage unit 242 to the third thermal storage unit 244 to maintain
a desired level of cooling fluid 33 (e.g., cold cooling fluid 144)
in the third thermal storage unit 244. Likewise, cooling fluid 33
(e.g., cold cooling fluid) flows from the first thermal storage
unit 240 to the second thermal storage unit 242 to maintain a
desired level of cooling fluid 33 (e.g., cold cooling fluid 144) in
the second thermal storage unit 242. The flow rate of cooling fluid
between the first, second, and third thermal storage units 240,
242, and 244 may be approximately the same, thereby maintaining the
initial volume of cooling fluid 33 within each thermal storage
unit. As may be appreciated, the each thermal storage unit may
stratify the cooling fluid 33 such that the cold cooling fluid 144
is near the bottom 49 to drain into the next thermal storage unit,
and the warm cooling fluid 146 is near the top 47.
[0057] The first thermal storage unit 240 fills with warm cooling
fluid 146 (e.g., warm water) from the one or more subcooling heat
exchangers 32 as the cold cooling fluid 144 (e.g., cold water)
drains to the top 47 of the second thermal storage unit 242 from
the bottom 49 of the first thermal storage unit 240. When the first
thermal storage unit 240 is full of warm cooling fluid 146,
additional warm cooling fluid 146 from the one or more subcooling
heat exchangers 32 leads warm cooling fluid 146 to flow from the
bottom 49 of the first thermal storage unit 240 to the top 47 of
the second thermal storage unit 242. Once the second thermal
storage unit 242 is full of the warm cooling fluid 146 (e.g., warm
water) and substantially empty of the cold cooling fluid 144,
additional warm cooling fluid 146 added to the second thermal
storage unit 242 leads warm cooling fluid 146 to flow from the
bottom 49 of the second thermal storage unit 242 to the top 47 of
the third thermal storage unit 244. Therefore, as the cold cooling
fluid 144 is sequentially drained from the first, second, and third
thermal storage units 240, 242, and 244 to flow through the one or
more subcooling heat exchangers 32, warm cooling fluid 146 from the
one or more heat exchangers 32 sequentially fills the first,
second, and third thermal storage units 240, 242, and 244 during
the subcooling mode. Eventually, warm cooling fluid 146 may fill at
least a portion of the third thermal storage unit 244 until a
recharge mode begins to cool at least a portion of the cooling
fluid 33.
[0058] As may be appreciated, the cooling system 10 of FIG. 10 may
have a similar arrangement of the first, second, third, and fourth
valves 38, 40, 42, and 44 as described above with FIG. 3. The first
valve 38 is between the cooler 24 and the load 14, the second valve
40 is between the cooler 24 and the thermal storage units 36, the
third valve 42 is between the thermal storage units 36 and the
chilled fluid pump 48, and the fourth valve is between the load 14
and the chilled fluid pump 48. Valves 246 allow for cooling fluid
33 to bypass one or more of the thermal storage units 240, 242, and
244 during a recharging mode. That is, the cooling fluid 33 of each
thermal storage unit 240, 242, and 244 may be recharged separately.
For example, if only the first thermal storage unit 240 contains
warm cooling fluid, then a fifth valve 248 between the second valve
40 and the first thermal storage unit 240 may open, and sixth and
seventh valves 250 and 252 may remain closed so as to allow for
cooling/recharging of only the cooling fluid 33 of the first
thermal storage unit 240. If the first thermal storage unit 240 is
full of warm cooling fluid 146, and the second thermal storage unit
242 is partially full of warm cooling fluid 146, then the fifth
valve 248 may be opened first to allow the cooling fluid 33 in the
first thermal storage unit 240 to cool down to a temperature near
the average temperature of the cooling fluid 33 in the second
thermal storage unit 242. Then, the sixth valve 250 between the
second valve 40 and the second thermal storage unit 242 may be
opened, and the fifth valve 248 may be closed to allow the first
thermal storage unit 240 and/or the second thermal storage unit 242
to be cooled or recharged. Similarly, once the first and second
thermal storage units 240 and 242 are cooled to a temperature near
the average temperature of the cooling fluid in the third thermal
storage unit 244, the fifth and sixth valves 248 and 250 may be
closed while the seventh valve 252 between the second valve 40 and
the third thermal storage unit 244 is opened to allow for cooling
or recharging of the third thermal storage unit 244, or each of the
first, second, and third thermal storage units 240, 242, and 244.
Operation of the valves 246, as discussed above, may be controlled
by an automation controller 52 based on measurements from sensors
(e.g., temperature sensors and level sensors) positioned in the
thermal storage units 240, 242, and 244. In some embodiments,
thermal storage units 36 in series may be utilized in a similar
manner to a stratified storage tank 138, as described in FIG. 5.
That is, separate thermal storage units 36 may be utilized rather
than the movable partition 142, where the separate thermal storage
units 36 may be used to at least partially separate the warm
cooling fluid 146 from the cold cooling fluid 144.
[0059] FIG. 11 is a schematic of an embodiment of the cooling
system 10 having the refrigerant circuit 20 and the subcooling
system 12, where the thermal storage unit 36 of the subcooling
system 12 includes multiple tanks to thermally isolate cold cooling
fluid 144 from warm cooling fluid 146. The thermal storage unit 36
may include a first tank 253, a second tank 254, and a third tank
255, as well as flow control valves 256 that may be controlled to
isolate the cooling fluid 33 flow for each tank. The first, second,
and third tanks 253, 254, and 255 may be horizontally arranged, as
shown in FIG. 11, or vertically arranged with the third tank 255
above the second tank 254, and the second tank 254 above the first
tank 253. In some embodiments, each tank of the first, second, and
third tanks 253, 254, and 255 may have a vent to the ambient
environment, thereby enabling the cooling fluid 33 within each tank
to be at approximately atmospheric pressure. In some embodiments,
each tank of the first, second, and third tanks 253, 254, and 255
may be pressurized above atmospheric pressure.
[0060] In some embodiments, the flow control valves 256 may be
controlled to enable the cooling fluid 33 in the second tank 254
and/or the third tank 255 to be recharged (e.g., cooled) while the
first tank 253 supplies cold cooling fluid 144 to the subcooling
heat exchanger 32 as shown by arrows 102. The first tank 253
supplies cold cooling fluid 144 to the subcooling pump 100 during
operation in a subcooling mode. The cold cooling fluid 144 absorbs
heat from the refrigerant 25 in the subcooling heat exchanger 32,
thereby exiting the subcooling heat exchanger 32 as warm cooling
fluid 146. The warm cooling fluid 146 from the subcooling heat
exchanger 32 flows to the third tank 255. Accordingly, during
subcooling mode, the first tank 253 has primarily cold cooling
fluid 144, and warm cooling fluid 146 is added to the third tank
355. As the cold cooling fluid 144 empties from the first tank 253
via the subcooling pump 100 through the subcooling heat exchanger
32, the first and second control valves 257, 258 may open to fill
the first tank 253 with any cold cooling fluid 144 from the second
tank 254. The first control valve 257 is between the second valve
40 and the first tank 253, and the second control valve 258 is
between the second valve 40 and the second tank 254. The third tank
255 may be approximately 30 to 50 percent larger than either the
first tank 253 or the second tank 254. In some embodiments, the
volume of cooling fluid in the first, second, and third tanks 253,
254, and 255 may be controlled to enable the total cooling fluid
volume may be held within the third tank 255, the subcooling
circuit 34, and one of first tank 253 or the second tank 255.
[0061] Warm cooling fluid 146 from the third tank 255 may be
directed to the second tank 254 as the third tank 255 fills with
warm cooling fluid 146 from the subcooling heat exchanger 32. For
example, a second control valve 258 and a third control valve 265
may open, the second valve 40 and a fifth control valve 267 may be
closed, and a transfer pump 259 may pump at least a portion of the
warm cooling fluid 146 from the third tank to the second tank 254,
as shown by arrow 103. The third control valve 265 along arrows
103, 105, and 109 between the third tank 255 and the transfer pump
259 or the third valve 42. Additionally, or in the alternative, the
third control valve 265 and a fourth control valve 266 may be
opened while the third valve 42 is closed to enable at least a
portion of the warm cooling fluid 146 from the third tank 255 to
the second tank 254, as shown by arrow 105. The fourth control
valve 266 is along arrows 103 and 105 between the second tank 254
and the transfer pump 259 or the third valve 42. Accordingly,
continued operation in the subcooling mode without recharge may
substantially fill the second and third tanks 254, 255 with warm
cooling fluid 146, while the first tank 253 is substantially
emptied of the cold cooling fluid 144.
[0062] As may be appreciated, the cooling system 10 of FIG. 11 may
have a similar arrangement of the first, second, third, and fourth
valves 38, 40, 42, and 44 as described above with FIG. 3. The first
valve 38 is between the cooler 24 and the load 14, the second valve
40 is between the cooler 24 and the thermal storage units 36, the
third valve 42 is between the thermal storage units 36 and the
chilled fluid pump 48, and the fourth valve is between the load 14
and the chilled fluid pump 48. During a recharge mode, the control
valves 256 and the first, second, third, and fourth valves 38, 40,
42, and 44 may be controlled to cool the cooling fluid 33 (e.g.,
warm cooling fluid 146) in the second tank 254 and the third tank
255 separately. For example, the first and fourth valves 38, 44 may
close and the second and third valves 40, 42 may open to fluidly
couple the subcooling circuit 34 with the cooler 24. To recharge
the cooling fluid of the second tank 254 upon coupling the
subcooling circuit 34 with the cooler 24, the second control valve
258 and fourth control valve 266 are opened, and the first, third,
and a fifth control valve 257, 265, and 267 are closed to enable
the flow shown by arrow 107. The fifth control valve 267 is between
the second valve 40 and the third tank 255. Therefore, the cooling
fluid 33 of the second tank 254 may be drawn toward the chilled
fluid pump 48, as shown by arrow 54, and pumped through the chiller
24 and back to the second tank 254, as shown by arrow 111, to
decrease the temperature of the cooling fluid within the second
tank 254. During the recharge of the cooling fluid 33 in the second
tank 254, the first tank 253 may simultaneously supply cold cooling
fluid 144 to the subcooling heat exchanger 32, thereby subcooling
the refrigerant 25 and increasing the warm cooling fluid 146 in the
third tank 255. When the cooling fluid 33 in the second tank 254
reaches a desired temperature (e.g., temperature of the cold
cooling fluid 144), the fourth control valve 266 may be closed, and
the first and second control valves 257, 258 are controlled to fill
the first tank 253 with the cooling fluid 33 from the second tank
254.
[0063] The warm cooling fluid 146 of third tank 255 may be
recharged via multiple valve configurations. In some embodiments,
at least a portion of the warm cooling fluid 146 of the third tank
255 may be transferred directly to the second tank 254, as
discussed above and shown by arrows 103 or 105. The warm cooling
fluid 146 received by the second tank 254 may then be recharged as
shown by arrows 107, 54, and 111. In some embodiments, the second
and third control valves 258, 265 may be opened while the first,
fourth, and a fifth control valve 257, 266, 267 are closed, thereby
enabling the flow shown by arrow 109. The chilled fluid pump 48
directs the warm cooling fluid 146 from the third tank 255, as
shown by arrows 109 and 54, through the cooler 24 and into the
second tank 254 as cold cooling fluid 144, as shown by arrow 111.
Moreover, in some embodiments, the third control valve 265 and the
fifth control valve 267 are opened while the first, second, and
fourth control valves 257, 258, and 266 are closed, thereby
enabling the flow shown by arrow 109. The chilled fluid pump 48
directs the warm cooling fluid 146 from the third tank, as shown by
arrows 109 and 54, through the cooler 24 and into the third tank
255 as cold cooling fluid 144, as shown by arrow 113. Any of the
above valve configurations may be utilized to cool the warm cooling
fluid 146 of the third tank 255. In some embodiments, cold cooling
fluid 144 from the first tank 253 may not flow through the
subcooling heat exchanger 32, such as by closing a sixth control
valve 268 between the first tank 253 and the subcooling pump 100,
thereby reducing the warm cooling fluid 146 added to the third tank
255 while the third tank 255 is recharged. Additionally, or in the
alternative, a seventh control valve 269, located between the sixth
control valve 268 and the third valve 42, may be opened to enable
cold cooling fluid 144 from the first tank 253 to be directed
through the cooler 24 with the warm cooling fluid 146. Accordingly,
the temperature of the cooling fluid 33 in the third tank 255 may
be decreased to a desired temperature (e.g., temperature of the
cold cooling fluid 144).
[0064] In some embodiments, the cooling fluid 33 of the third tank
255 may be cooled while subcooling the refrigerant 25 without
adding warm cooling fluid 146 to the cooling fluid 33 that is being
cooled in the third tank 255. For example, a fourth tank 270 may
receive the warm cooling fluid 146 from the subcooling heat
exchanger 32 while the third tank 255 is recharged. In another
embodiment, the third tank 255 may be a stratified fluid tank with
a partition as described above, thereby enabling the warm cooling
fluid 146 entering the third tank 255 to be separated from the
cooling fluid 33 being recharged. In another embodiment, the
subcooling heat exchanger 32 may not receive cold cooling fluid 144
from the first tank 253 while recharging the third tank 255.
Accordingly, the first, second, and third tanks 253, 254, and 255
may be utilized to reduce or eliminate mixing of cold cooling fluid
144 with warm cooling fluid 146 within any particular tank.
[0065] FIG. 12 is a schematic of an embodiment of the cooling
system 10 having the refrigerant circuit 20 and the subcooling
system 12, where the thermal storage unit 36 does not include a
tank. More specifically, the thermal storage unit 36 in the
illustrated embodiment includes a ground loop 260 (e.g., a
subterranean conduit or conduit below a surface 264 of the earth
which carries the cooling fluid 33). In certain embodiments, the
ground loop 260 may thermally isolate warm cooling fluid 146 and
cold cooling fluid 144 to improve thermal storage capability. For
example, the ground loop 260 may include a horizontal loop or
multiple vertical loops 262 in series to help thermally isolate
warm cooling fluid 146 and cold cooling fluid 144. As may be
appreciated, the cooling system 10 of FIG. 12 may have a similar
arrangement of the first, second, third, and fourth valves 38, 40,
42, and 44 as described above with FIG. 3. The first valve 38 is
between the cooler 24 and the load 14, the second valve 40 is
between the cooler 24 and the ground loop 260, the third valve 42
is between the ground loop 260 and the chilled fluid pump 48, and
the fourth valve is between the load 14 and the chilled fluid pump
48.
[0066] FIG. 13 is a schematic of an embodiment of the cooling
system 10 having the refrigerant circuit 20 and the subcooling
system 12, where the subcooling system 12 is a "once-through"
system. In other words, the illustrated embodiment of the
subcooling system 12 directs a cooling fluid 33 (e.g., water)
through the subcooling system 12 once, and the cooling fluid 33 is
not necessarily re-circulated. For example, the cooling fluid 33
(e.g., water) may be supplied by a fluid source 280, such as ground
water or municipal water. The cooling fluid 33 exiting the
subcooling heat exchanger 32 as warm cooling fluid 146 may be used
for other applications. For example, the warm cooling fluid 146 may
flow to a water heater 282 to heat further or to preheat water, to
a reservoir 284 for present or future use with an irrigation system
286, or other uses. As will be appreciated, the illustrated
embodiment may be particularly applicable in environments or
locations where a fluid source of cold cooling fluid 144, such as
cool ground water, is available and/or abundant.
[0067] FIG. 14 is a schematic of an embodiment of the cooling
system 10 having the multiple refrigerant circuits 20 and the
subcooling system 12. The multiple refrigerant circuits 20 has
multiple coolers 24, and the subcooling system 12 has multiple
subcooling heat exchangers 32. In some embodiments, the coolers 24
may be fluidly coupled in the respective one or more refrigerant
circuits 20 in a parallel configuration, as shown by coolers 312
and 314. Additionally, or in the alternative, the subcooling heat
exchangers 32 may be coupled in the respective one or more
refrigerant circuits 20 in a parallel configuration, as shown by
subcooling heat exchangers 340 and 342. As may be appreciated, the
coolers 24 and subcooling heat exchangers 32 may be fluidly coupled
to the one or more refrigerant circuits 20 and/or to the subcooling
system 10 in various configurations. Accordingly, the cooling
system 10 may have additional flexibility in connecting different
subcooling heat exchangers 32 to the thermal storage unit 36 for
subcooling the refrigerant 25, additional flexibility in connecting
different coolers 24 to the load 14 for cooling the load 14, and/or
additional flexibility in connecting different coolers 24 to the
thermal storage unit 36 for recharging the cooling fluid 33.
[0068] For example, if valves 300 and 302 are closed and valves
304, 306, 308, and 310 are opened, then each of the coolers 312,
314, and 316 is coupled to the load 14 to cool the load fluid 22,
and each of the coolers 312, 314, and 316 is isolated from the
thermal storage unit 36. As shown, each of the coolers 312, 314,
and 316 has a corresponding load pump 318, 320, and 322,
respectively, and a corresponding check valve 324, 326, and 328,
respectively, to provide a fluid (e.g., load fluid 22, cooling
fluid 33) flow through each cooler 312, 314, and 316. Additionally,
a supply pump 330 may move load fluid 22 to the load 14. Subcooling
pumps 332, 334, and 336 pump cooling fluid 33 (e.g., water) from
the thermal storage unit 36 to the subcooling heat exchangers 32,
which are in refrigerant circuits 20 with the coolers 312, 314, and
316 as discussed above. For example, the subcooling pump 332 may
supply cooling fluid 33 to a subcooling heat exchanger 32 that is
fluidly coupled to the cooler 316, the subcooling pump 334 may
supply cooling fluid 33 to a subcooling heat exchanger 32 that is
fluidly coupled to the coolers 314 and 312, and the subcooling pump
336 may supply cooling fluid 33 to a subcooling heat exchanger 32
that is fluidly coupled to the coolers 314 and 316. In certain
embodiments, check valves 338, 340, and 342 may also be included
with the subcooling loops.
[0069] The cooling system 10 illustrated in FIG. 14 may enable the
cooling fluid 33 of the thermal storage unit 36 to be
simultaneously recharged via one or more coolers 312, 314, and 316
while subcooling the refrigerant 25 of one or more refrigerant
circuits 20 via one or more subcooling heat exchangers 32. In other
words, the cooling system 10 may operate in the recharge mode and
subcooling mode at the same time. In the illustrated embodiment,
the thermal storage unit 36 (e.g., water tank) may be recharged
using cooler 316 by closing valves 308 and 310 and opening valves
300 and 302, thereby isolating the thermal storage unit 36 from the
coolers 312 and 314. As will be appreciated, to provide pressure
isolation, valves 308 and 310 should be closed before valves 300
and 302 are opened. This configuration allows for cooler 316 to
cool the cooling fluid 33 (e.g., water) in the thermal storage unit
36 while coolers 312 and 314 supply load fluid 22 (e.g., chilled
water) to the load 14. Similarly, valves 304 and 306 can be closed
while valves 300, 302, 308, and 310 are opened, thereby isolating
the thermal storage unit 36 from the cooler 312. In such a
configuration, coolers 314 and 316 may cool the cooling fluid 33 in
the thermal storage unit 36, while cooler 312 supplies load fluid
22 (e.g., chilled water) to the load 14.
[0070] FIG. 15 is a schematic of an embodiment of the cooling
system 10 having a refrigerant loop 350 and the subcooling system
12, where the subcooling system 12 may be suitable for
trans-critical operation of the refrigerant 25 through the
refrigerant loop 350. As may be appreciated, a trans-critical
process may cool the refrigerant 25 to a subcooled (e.g., liquid)
state, and may heat and/or pressurize the refrigerant 25 to a
supercritical state where liquid and gas phases of the refrigerant
25 are indistinguishable. For example, in the illustrated
embodiment, the cooling system 10 has a refrigerant loop 350, and
the subcooling system 12 has a first cooling fluid (e.g., water)
loop 352 and a second cooling fluid (e.g., water) loop 354. Similar
to the refrigerant circuit 20 described above, the refrigerant loop
350 circulates a refrigerant 25 (e.g., carbon dioxide, R134a,
R410A, R32, R1233ZD(E), R1233zd (E), R1234yf, R1234ze) and includes
the cooler 24, the compressor 26, the subcooling heat exchanger 32,
and the expansion device 30. The cooler 24 may be utilized to
recharge the cooling fluid 33 (e.g., water) of the thermal storage
unit 36. The illustrated refrigerant loop 350 includes a condenser
coil 356 as the condenser 28, and a condenser fan 358 is configured
to move air over the condenser coil 356, thereby cooling the
refrigerant 25. The refrigerant loop 350 also includes an
evaporator coil 360, in which the refrigerant 25 absorbs heat and
at least partially evaporates. In some embodiments, the load fluid
22 (e.g., return water 45) from the load 14 circulates through the
evaporator 360 to transfer heat to the refrigerant 25. An
evaporator fan 362 may be configured to move air over the
evaporator coil 360, thereby cooling the air and transferring heat
to the refrigerant 25. In some embodiments, the air moving over the
evaporator coil 360 is the load, such as in a refrigeration
system.
[0071] A first cooling fluid loop 352 may subcool the refrigerant
25 of the refrigerant loop 350 via the subcooling heat exchanger
32. For example, the first cooling fluid loop 352 supplies the
cooling fluid 33 (e.g., cold water) from a lower tank 366 to the
subcooling heat exchanger 32 and to an upper tank 368 via a first
pump 364. A second cooling fluid loop 354 may be cool (e.g.,
recharged) via circulation through the cooler 24. For example, the
second cooling fluid loop 354 supplies the cooling fluid 33 (e.g.,
water) from the lower tank 366 to the cooler 24, and back to the
lower tank 366. The thermal storage unit 36 may include the lower
tank 366 and the upper tank 368, where the upper tank 368 is
arranged vertically above the lower tank 366. Specifically, the
first cooling fluid loop 352 includes a first pump 364 configured
to pump the cooling fluid 33 through the first cooling fluid loop
352. That is, the first pump 364 draws the cooling fluid 33 from a
bottom 365 of the lower tank 366 of the thermal storage unit 36,
pumps the cooling fluid 33 through the subcooling heat exchanger
32, and discharges the warmed cooling fluid 33 into the upper tank
368 of the thermal storage unit 36. A valve 370 is located between
the lower tank 366 and the upper tank 368 to complete the first
cooling fluid loop 352. Similarly, the second cooling fluid loop
354 includes a second pump 372 configured to pump the cooling fluid
33 through the second cooling fluid loop 354. Specifically, the
second pump 372 draws cooling fluid 33 (e.g., water) from the
bottom 365 of the lower tank 366, pumps the cooling fluid 33
through the cooler 24, and discharges the cooling fluid 33 back
into the lower tank 366.
[0072] During a discharge (e.g., cooling) mode of the illustrated
embodiment, the refrigerant 25 in the evaporator 360 absorbs heat
from the load 14. The compressor 26 increases the pressure of the
refrigerant 25 and directs the refrigerant 25 through the condenser
356 to reject heat to the air drawn by the condenser fan 358. The
first pump 364 moves cold cooling fluid 144 (e.g., cold water) from
the bottom 365 of the lower tank 366, through the subcooling heat
exchanger 32, and into the upper tank 368, thereby further cooling
the refrigerant 25 before expansion by the expansion device 30. An
air vent 374 of the thermal storage unit 36 enables air to move
freely from a top 375 of the upper tank 368 to a 377 top of the
lower tank 366, such that the level of the cold cooling fluid 144
in the lower tank 366 drops as the first pump 364 fills the upper
tank 368 with warm cooling fluid 146 from the subcooling heat
exchanger 32.
[0073] At the beginning of the recharge mode of the illustrated
embodiment, the valve 370 may open between the upper tank 368 and
the lower tank 366, thereby enabling warm cooling fluid 146 from
the upper tank 368 to drain to the lower tank 366. During the
recharge mode, the refrigerant 25 through the refrigerant loop 350
may be utilized to primarily cool the cooling fluid 33 through the
cooler 24 rather than to remove heat from the load 14. For example,
as the warm cooling fluid 146 drains, the evaporator fan 362 may be
turned off, and the second pump 372 may be turned on to move warm
cooling fluid 146 from the lower tank 366, through the cooler 24,
and back to the lower tank 366, thereby reducing the temperature of
the cooling fluid 33 within the lower tank 366. In some
embodiments, the first pump 364 may continue to direct cooling
fluid 33 through the first cooling fluid loop 352 and the
subcooling heat exchanger 32 during the recharge mode, thereby
sending warm cooling fluid 146 to the upper tank 368. Upon draining
a desired amount (e.g., 25, 50, 75, 100 percent) of the warm
cooling fluid 146 from the upper tank 368, the valve 370 may be
closed, and the warm cooling fluid 146 leaving the subcooling heat
exchanger 32 may then accumulate in the upper tank 368 during the
remainder of the recharge process. Once the lower tank 366 is
cooled to a desired minimum temperature by circulating the cooling
fluid through the second cooling fluid loop 354, the recharging
process may be complete. Upon completion of the recharging process,
a majority of the cooling fluid 33 may be in the lower tank 366 as
cold cooling fluid 144, with the remainder of the cooling fluid 33
being warm cooling fluid 146 in the upper tank 368.
[0074] As will be appreciated, the operation of the cooling system
10 and the subcooling system 12 in discharge or recharge mode may
depend on various factors. For example, for systems where thermal
storage is lower priority, the sizes of the upper and lower tanks
368 and 366 may be relatively small, thereby enabling the cooling
system 10 to operate in the discharge mode for a brief time (e.g.,
approximately 1 hour or less). In such circumstances, it may be
desirable to initiate a recharge mode when the cooling fluid level
in the lower tank 366 reaches a minimum value. However, in
embodiments where thermal storage is higher priority, the upper and
lower tanks 368 and 366 may be relatively large and may be able to
operate in a discharge mode for several hours without recharging.
In such circumstances, the recharge mode may be initiated at night
or other times when energy rates are reduced.
[0075] Furthermore, in certain embodiments, as discussed above, the
thermal storage unit 36 may include a single tank (e.g., stratified
fluid tank 138). As will be appreciated, such embodiments may
utilize less space and may have lower initial equipment costs. In a
single tank embodiment, the first cooling fluid loop 352 may
discharge cooling fluid back to the top of the lower tank 366, such
as above a moveable partition.
[0076] FIG. 16 is a schematic pressure-enthalpy diagram for the
refrigerant 25 of the refrigerant loop 350 in the cooling system
shown in FIG. 15. Specifically, loop 400 shows pressure and
enthalpy of the refrigerant 25 of the refrigerant loop 350 when the
cooling system 10 is operating in a discharge mode, where the
subcooling system 12 cools the refrigerant 25 via the subcooling
heat exchanger 32. Moreover, loop 402 illustrates the pressure and
enthalpy of the refrigerant 25 of the refrigerant loop 350 when the
cooling system 10 is beginning to recharge the cooling fluid 33 of
the subcooling system 12. As shown by loop 402, the refrigerant 25
may remain gaseous (e.g., outside the saturated vapor curve)
throughout the loop 402. Loop 404 illustrates the pressure and
enthalpy of the refrigerant 25 of the refrigerant loop 350 during a
middle of the recharge of the cooling fluid 33 of the subcooling
system 12, where the refrigerant 25 may change phases within the
loop 404. Loop 406 illustrates the pressure and enthalpy of the
refrigerant 25 of the refrigerant loop 350 near an end of the
recharge of the cooling fluid 33 of the subcooling system 12. For
comparison, loop 408 illustrates a conventional trans-critical
vapor compression cycle without the subcooling system 12.
[0077] As will be appreciated, the cooling system 10 with the
refrigerant loop 350 and the subcooling system 12 illustrated in
FIG. 15 may reduce losses associated with the expansion process.
More specifically, during the discharge mode the cooling fluid 33
of the subcooling system 12 may be used to cool the trans-critical
refrigerant fluid 25 of the refrigerant loop 350 via the subcooling
heat exchanger 32 to a temperature that is near the evaporating
temperature of the trans-critical refrigerant 25. The energy in the
cooling fluid 33 is then rejected to the refrigerant 25 via the
cooler 24 during the recharge mode, and the refrigerant 25 rejects
the heat to the air via the condenser 356. Furthermore, the upper
and lower tank 368 and 366 configuration of the embodiment shown in
FIG. 15 may be incorporated with other embodiments described
herein.
[0078] In the case of trans-critical operation there is no phase
change (e.g., gas to liquid) in the condenser 356, and the
subcooler 32 cools a trans-critical refrigerant 25 instead of
subcooling a condensed liquid refrigerant. That is, the liquid
cooling fluid may cool the trans-critical refrigerant fluid 25 in
the subcooler 32. In addition it is possible to operate the
evaporator 360 and the expansion device 30 when the temperature of
the evaporator 360 exceeds the critical temperature of the
refrigerant 25. Loop 402 in FIG. 16 is an example of this extreme
operating condition where the refrigerant 25 does not condense.
Therefore the names of the components (e.g., evaporator 360,
condenser 356) are intended to broadly include operation at
conditions that exist at or above the refrigerant critical
point.
[0079] FIG. 17 is a schematic of an embodiment of the cooling
system 10 having the refrigerant circuit 20 and the subcooling
system 12, where the subcooling system 12 utilizes ice storage. In
this embodiment, melted water from an ice storage tank 420 (e.g.,
thermal storage unit 36) is used for subcooling. Specifically, a
subcooling pump 422 moves cold water 423 from a bottom 425 of the
ice storage tank 420, through the subcooling heat exchanger 32, and
back to a top 427 of the ice storage tank 420. In certain
embodiments, the flow rate of the subcooling pump 422 may be
selected to create a stratified ice storage tank. That is, the flow
rate may be slow so as to preserve the stratification of the ice
storage tank 420. Additionally, a glycol solution or other
anti-freeze liquid may be circulated through coils 424 in the ice
storage tank 420 to produce ice. Specifically, valves 426 and 428
may be configured to regulate the glycol or other anti-freeze
liquid flow.
[0080] During a recharge mode, valve 426 between the ice storage
tank 427 and a glycol pump 423 closes glycol flow to the load 14
and directs it to a bypass line 430 and to the glycol pump 432, as
indicated by arrow 434. Additionally, in the recharge mode, valve
428 between the cooler 24 and the ice storage tank 427 directs
glycol through the coils 424 in the ice storage tank 420, as
indicated by arrow 436. The recharge mode may freeze the cold water
423 to ice. In a discharge mode (e.g., cooling using melted ice
water 423), the valve 426 is open to the load 14 and closed to the
bypass line 430, as indicated by arrow 438. Additionally, valve 428
remains open to the coils 424 in the ice storage tank 420. Once the
ice in the ice storage tank 420 has melted, valve 428 closes glycol
flow to the coils 424 in the ice storage tank 420. At this point,
the subcooling pump 422 can be operated to provide additional
cooling (e.g., to the subcooling heat exchanger 32) using cold
water (e.g., melted ice water 423) from the bottom of the ice
storage tank 420, in the manner described above.
[0081] FIG. 18 is a schematic of an embodiment of the cooling
system 10 having the refrigerant circuit 20 and the subcooling
system 12, where the subcooling system 12 has two thermal storage
units 36 connected in parallel during recharge mode and connected
in series in subcooling mode. In the subcooling mode, warm cooling
fluid 450 from the subcooling heat exchanger 32 enters near the top
47 of a first thermal storage unit 452 at a low flow rate to enable
stratification of the cooling fluid 33 into a warm layer 454 and a
cool layer 456. Cold cooling fluid 33 exits the first thermal
storage unit 452 near the bottom 49 of the first thermal storage
unit 452 through an inclined pipe 458 and enters the second thermal
storage unit 460 near the top 47, as shown by the solid arrows 462.
Cold cooling fluid 33 exits near the bottom 49 of the second
thermal energy storage unit 404 to the subcooling pump 100. The
conduits carrying the cooling fluid 33 during the subcooling mode
are sized to enable the stratification of the first and the second
thermal energy storage units 452, 460 via a relatively low flow
rate. The arrangement of the inclined pipe 458 fluidly couples the
first and second thermal storage units 452, 460 in series during
the subcooling mode without utilizing valves to control the flow
between the first and second thermal storage units 452, 460.
[0082] In the recharge mode, cooling fluid 33 flows from the first
and/or the second thermal storage units 452, 460 as shown by the
dashed arrows 54. Chilled cooling fluid 33 from the cooler 24
enters through the inclined pipe 458 and may split to flow to flow
into the first and the second thermal energy storage units 452 and
460. A first recharge valve 464 coupled to the first thermal
storage unit 452 may control the recharged (e.g., chilled) flow of
cooling fluid 33 into the first thermal storage unit 452, and a
second recharge valve 466 coupled to the second thermal storage
unit 460 may control the recharged (e.g., chilled) flow of cooling
fluid 33 into the second thermal storage unit 460. As may be
appreciated, the chilled fluid pump 48 may direct the recharged
chilled fluid 33 into the first and second thermal storage units
452, 460 at a higher flow rate than the subcooling pump 100,
thereby mixing the cooling fluid within the first and second
thermal storage units 452, 460 during the recharge mode. Cooling
fluid 33 exits the first and second thermal storage units 452, 460
through a conduit 468, and the chilled fluid pump 48 directs the
combined cooling fluid flow through the chiller 24. A third
recharge valve 470 coupled to the first thermal storage unit 452
may control the flow of cooling fluid 33 from the first thermal
storage unit 452 to the chilled fluid pump 48, and a fourth
recharge valve 472 coupled to the second thermal storage unit 460
may control the flow of cooling fluid 33 from the second thermal
storage unit 460 to the chilled fluid pump 48. The first, second,
third, and fourth recharge valves 464, 466, 470, and 472 may be
selectively opened and closed to recharge the first thermal storage
unit 452 and the second thermal storage unit 460 at the same time.
Additionally, or in the alternative, the first, second, third, and
fourth recharge valves 464, 466, 470, and 472 may be selectively
opened and closed to recharge only the first thermal storage unit
452 or only the second thermal storage unit 460. While the first
and second recharge valves 464, 466 are shown on the inclined pipe
458, it may be appreciated that other arrangements of the first and
second recharge valves 464, 466, such as within the respective
first and second thermal storage units 452, 460, may enable the
recharge of one or both of the thermal storage units 452, 460.
Likewise, while the third and fourth recharge valves 470, 472 are
shown on the conduit 468, it may be appreciated that other
arrangements of the third and fourth recharge valves 464, 466, such
as within the respective first and second thermal storage units
452, 460, may enable the recharge of one or both of the thermal
storage units 452, 460. The first, second, third, and fourth
recharge valves 464, 466, 470, and 472 may be include, but are not
limited to butterfly valves. Similar configurations of recharge
valves, inclined pipes, and conduits can be extended to more than
two thermal storage units.
[0083] In some embodiments, the conduit 468 may be coupled between
the first thermal storage unit 452 and the second thermal storage
unit 460 in a similar manner as the inclined pipe 458. That is, the
conduit 468 may form a substantially parallel pathway to the
inclined pipe 458 in which a first end of the conduit 468 is
coupled near the bottom 49 of the first thermal storage unit 452
and an opposite second end of the conduit 468 is coupled near the
top 47 of the second thermal storage unit 460. This inclined
configuration of the conduit 468 may enable the removal of the
third and fourth recharge valves 470, 472. In the subcooling mode,
the cooling fluid 33 from the bottom of the first thermal storage
unit 452 may flow through the conduit 468 and the inclined pipe 458
to a location near the top 47 of the second thermal storage unit
460, as shown by the solid arrows 462. This inclined configuration
of the conduit 468 enables warm cooling fluid 33 to fill the first
thermal storage unit 452 and cold cooling 33 to flow through the
inclined pipe 458 and the conduit 468 to the second thermal storage
unit 460, such that the warm layer 454 substantially fills the
first thermal storage unit 452. When the first thermal storage unit
452 is filled with warm cooling fluid, warm cooling fluid 33 may
flow through the inclined pipe 458 and the conduit 468 to form a
stratified warm layer 454 and a cool layer 456 of cooling fluid 33
in the second thermal storage unit 460. In the recharge mode, the
cooled cooling fluid 33 from the cooler 24 may flow into the first
and second thermal storage units 452, 460 through the inclined pipe
458, and the cooling fluid 33 may flow from the first and second
thermal storage units 452, 460 through the conduit 468 to be
recharged (e.g., cooled) via the cooler 24. The inclined
configuration of the conduit 468 may enable the removal of the
third and fourth recharge valves 470, 472 to control flow during
subcooling and recharge modes. As may be appreciated, some valves
may be utilized to enable servicing or replacement of thermal
storage units 36 and piping while operating with the remaining one
or more thermal storage units 36. Additionally, or in the
alternative, valves may be utilized for balancing flow between the
first and second thermal storage units 452, 460 during recharge
mode.
[0084] As will be appreciated, the systems and embodiments
described above may include variations in components,
configurations, operating parameters, and so forth, which may
depend on the particular application of the cooling system 10 with
the refrigerant circuit 20 and the subcooling system 12. For
example, the compressors 26 described above may be configured for
use with varying suction pressures. Such compressors 26 may include
variable-speed centrifugal compressors, variable-speed
reciprocating compressors, variable-stroke linear compressors,
compressors with magnetic bearings, and so forth. For reciprocating
and linear compressors, the discharge valve naturally compensates
for changes in pressure ratio. Additionally, at high suction
pressure, it may be desirable to reduce compressor capacity to
prevent overload of the rest of the cooling system 10. Reduced
compressor speed or reduced piston stroke also prevents overloading
the suction and discharge valves for the reciprocating and linear
compressors.
[0085] Furthermore, in addition to including the subcooling heat
exchanger 32 in the refrigerant circuit (e.g., refrigerant circuit
20, refrigerant loop 350) of the cooling system 10, it may be
desirable to make other modifications to the cooling system 10. For
example, a subcooling section from the condenser 28 may be removed,
which may allow more space for condensation and/or a reduction in
condenser 28 size and cost. For air-cooled condensers, reducing the
refrigerant charge in the condenser 28 may have a similar effect.
For other cooling systems 10, it may be desirable to eliminate
economizers to reduce costs, to reduce compressor 26 load during
peak conditions, and/or to increase the energy storage capacity of
the thermal storage unit 36 of the subcooling system 12. Likewise,
it may be desirable to eliminate intercoolers found in multi-stage
centrifugal compressors or other multi-stage systems.
[0086] As described above, the cooling fluid flow rate of the
subcooling system 12 may be optimized to maximize efficiency of the
subcooling system 12 to cool the refrigerant 25 of the refrigerant
circuit 20 of the cooling system 10. In certain embodiments, the
cooling fluid flow rate through the subcooling heat exchanger 32
may be selected such that the temperature change of the cooling
fluid 33 across the subcooling heat exchanger 32 may be
approximately equal to the temperature change of the refrigerant 25
across the subcooling heat exchanger 32. In some embodiments, the
cooling fluid flow rate through the subcooling heat exchanger 32
may be selected such that the cooling fluid 33 exiting the
subcooling heat exchanger 32 is approximately the same temperature
as the refrigerant 25 entering the subcooling heat exchanger 32,
and the refrigerant 25 exiting the subcooling heat exchanger 32 is
approximately the same temperature as the cooling fluid 33 entering
the subcooling heat exchanger 32.
[0087] Additionally, as described with reference to FIG. 2 above,
the system may include a variety of sensors 50 and a controller 52
(e.g., an automation controller, programmable logic controller,
distributed control system, etc.) configured to operate various
components (e.g., valves) based on feedback measured by the sensors
50. It should be appreciated that the sensors 50 and controller 52,
as well as other sensors and controllers, may be used with any of
the embodiments described herein. For example, the sensors 50 may
be configured to measure temperatures, pressures, flow rates, or
other operating parameters of the refrigerant circuit 20 and/or the
subcooling system 12. Additionally, the controller 52 may be
configured to operate any of the components (e.g., valves, pumps)
described herein or other components based on measured
feedback.
[0088] As discussed above, the refrigerant circuit 20 and the
subcooling systems 12 described herein may improve efficiency of
the cooling system 10. Additionally, certain embodiments described
above may have lower costs (e.g., first costs and/or operating
costs) than other systems. For example, equipment costs, energy
costs, maintenance costs, and other costs may be reduced. In some
embodiments, thermal storage units 36 may reduce the foot print at
a worksite utilized for a given cooling load. For example, a
cooling system with a 10,000 ton capacity utilizing radiators
rather than thermal storage units may have a foot print of
approximately 38,220 ft.sup.2, whereas a cooling system 10 with a
10,000 ton capacity as described above utilizing three thermal
storage units 36 (e.g., 42 ft diameter, 30 ft height) and radiators
may have a foot print of approximately 28,179 ft.sup.2, which is
approximately 24 percent smaller. Combinations of one or more of
the disclosed embodiments may also be used. The various tank and
piping configurations may be combined and may be desirable to meet
the requirements of particular applications.
[0089] The cooling fluid 33 referenced in the embodiments described
above may include primarily water. In some embodiments, the cooling
fluid 33 may include water with a biocide and/or corrosion
inhibitors. Propylene or ethylene glycol or other antifreeze can
also be added to provide freeze protection. Non-aqueous liquids,
slurries, etc. are also options for the cooling fluid 33. In some
embodiments with stratified thermal storage units 36 having
water-based solutions of cooling fluid 33, an additive that reduces
the temperature of minimum density of the cooling fluid 33 may be
utilized where the temperature of the cooling fluid 33 may be below
approximately 39.degree. F.
[0090] With regard to the piping forming the loops and flow paths
discussed above, in freezing climates without antifreeze, exposed
piping should be insulated and heat-traced to prevent possible
freezing damage. The thermal storage units 36 may be open and may
be naturally resistant to freezing damage, although heaters or
insulation may be desirable in some cases.
[0091] It should be noted that certain embodiments described here
can also be used as a heat pump for heating applications. A
distinction between employing present embodiments as a heating
system rather that cooling is that heat leaving the condenser is
considered the primary output, although the system can
simultaneously provide cooling as a useful output. A variation for
heat pumps is to cool refrigerant liquid using incoming ventilation
air either directly or through a secondary (glycol) loop.
[0092] While only certain features and embodiments have been
illustrated and described, many modifications and changes may occur
to those skilled in the art (e.g., variations in sizes, dimensions,
structures, shapes and proportions of the various elements, values
of parameters (e.g., temperatures, pressures, etc.), mounting
arrangements, use of materials, colors, orientations, etc.) without
materially departing from the novel teachings and advantages of the
subject matter recited in the claims. The order or sequence of any
process or method steps may be varied or re-sequenced according to
alternative embodiments. It is, therefore, to be understood that
the appended claims are intended to cover all such modifications
and changes as fall within the true spirit of the invention.
Furthermore, in an effort to provide a concise description of the
exemplary embodiments, all features of an actual implementation may
not have been described (i.e., those unrelated to the presently
contemplated best mode of carrying out the invention, or those
unrelated to enabling the claimed invention). It should be
appreciated that in the development of any such actual
implementation, as in any engineering or design project, numerous
implementation specific decisions may be made. Such a development
effort might be complex and time consuming, but would nevertheless
be a routine undertaking of design, fabrication, and manufacture
for those of ordinary skill having the benefit of this disclosure,
without undue experimentation.
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